CDMA demodulating apparatus

ABSTRACT

A CDMA demodulating apparatus with an improved interference canceling effect when there are a large number of communicators. A reception signal having a frame configuration in which a pilot signal of a known pattern is inserted between information signals is received from a plurality of communicators. Transmission data of each communicator is demodulated, an interference canceler for estimating is provided in a plurality of stages, in each channel of each stage, a variation of transmission path is estimated in each path to achieve data demodulation and estimation of interference replica. The later the stage, the more error of interference signal replica can be reduced, thereby improving the interference canceling effect. An even better effect can be obtained when interference canceling is performed after detecting a reception level of each channel by summation of reception power of each path of each channel, and channel ranking is determined in the order of higher reception level.

TECHNICAL FIELD

The present invention relates to a code division multiple access (CDMA)demodulating apparatus used for receiving signals of a CDMA system usingspread spectrum, and more specifically to a CDMA demodulating apparatussuitable for a mobile communication system which uses a cellularconfiguration.

BACKGROUND ART

DS (Direct Sequence)--CDMA is a system in which a plurality of userscarry out communications using a same frequency band, and each user isidentified by a spreading code. As a spreading code for each user, aspreading code such as Gold code is used. Interference signal power ofanother user is a reciprocal of average spreading factor (PG) in thedespreading process of a receiver. However, each user, especially underasynchronous environment in ascendant mobile communications, is subjectto momentary variation, short section variation, and distance variationdue to independent fading.

Therefore, to satisfy a predetermined reception quality determined bythe system by each user at the receiving side, it is necessary tocontrol the transmission power to achieve a constant SIR(Signal-to-Interference Ratio) in the receiver input at the basestation. Here, SIR is a ratio of the reception signal power at the userof the desired wave to the interference signal power received fromanother user. However, even though the transmission power control isperfect, and the SIR in the base station receiver input is maintained ata constant value, under multipath environment of mobile communications,spreading codes will never quadrate completely with each other.Therefore, the user is subject to interference due to cross-correlationof the power of a reciprocal of spreading factor at an average per oneof other users.

As shown above, since the interference signal level increases withincreasing number of users communicating in the same frequency band, toincrease the user capacity per cell, an interference canceling techniqueto reduce interference from other users is required.

As interference canceling techniques, a multi-user type interferencecanceler and a single user type interference canceler are known. Themulti-user type interference canceler not only demodulates a desiredwave signal of its own channel, but also demodulates a signal of anotheruser using spreading code information and reception signal timing of theother user. The single user type interference canceler, on the otherhand, uses only the spreading code of own channel to minimize an averagecross-correlation and noise component from the other user.

The multi-user type canceler includes a linear processing type(decorrelator or the like) and a nonlinear processing type. Thedecorrelator calculates mutual correlation of the spreading code of ownchannel and all other spreading codes of receiver input to determine aninverse matrix composed of the cross-correlation, and thecross-correlation is canceled by compensating for the output signal of amatched filter using this inverse matrix. Where K is a number of users,and Lk is a number of reception paths to individual users, dimension Dmof the decorrelator matrix is given by the following equation. ##EQU1##

Therefore, realization of the above technique becomes difficult as thenumber of users increases, which increases the circuit scale.

A nonlinear multi-user type interference canceler is a replicareproduction type interference canceler. This canceler demodulatesinterference signal from other user's channel, decides it to reproducetransmission information data replica, calculates an interference signalreplica of each channel from this replica, and subtracts theinterference replica from the reception signal, thereby demodulating thedesired wave signal with enhanced SIR.

FIG. 1 shows a replica reproduction type multi-stage interferencecanceler (serial interference canceler) proposed in the document "Serialinterference cancellation method for CDMA", IEE, Electronics LettersVol. 30, No. 19, pp. 1581-1582, Sept. 1994.

In FIG. 1, the numeral 11 indicates a spread signal, 12, 16 are delayunits, 13, 17 are matched filters, 14, 18 are respreaders, and 15 is ainterference subtractor. The serial canceler comprises interferencecanceling blocks in a plurality of stages, connected in series, wherebythe interference canceling blocks of individual stages carry outdemodulation and generation of interference signal replica by turns to Musers to be demodulated.

The receiver first rearranges the reception signals in the order ofreception signal level. For explanation, serial numbers from 1 to M areassigned to the rearranged signals, number 1 being assigned to thehighest reception signal level. The interference canceling block of thefirst stage makes despreading, demodulation and data decision by thematched filter 13 on the reception signal of number 1, and the resultingreproduction data is referred to as D₁.sup.(1). The respreader 14calculates an interference signal replica S₁.sup.(1) of this channelfrom the reproduction data D₁.sup.(1). The interference subtractor 15subtracts the interference signal replica from a reception signal Spassed through the delay unit 16. The matched filter 17 makesdespreading, demodulation and data decision on the signal obtained bythe subtraction using the spreading code replica of user 2 to obtain areproduction data D₂.sup.(1) of user 2. The matched filter input signalof user 2 is improved in SIR to the extent that the interference signalreplica S₁.sup.(1) of user 1 is subtracted as compared with directdespreading from the reception signal S.

Similarly, to user 2, an interference signal replica S₂.sup.(1) isobtained from the reproduction data. A matched filter input signal ofuser 3 is obtained by subtracting interference signal replicas of users1 and 2 from the reception signal S passed through the delay unit. Usingthis procedure, for subsequent users, the reception SIR can be furtherenhanced. When despreading the reception signal of M'th user,interference signal replicas S₁.sup.(1) +S₂.sup.(1) +. . .S_(M-1).sup.(1) of a total of (M-1) users are subtracted from thereception signal S to produce a signal, thereby considerably improvingthe SIR over the reception signal S. As a result, demodulated signal ofM'th channel is improved in reliability.

Using interference signal replicas S₁.sup.(1), S₂.sup.(1), . . . ,S_(M-1).sup.(1) of individual users estimated in the first stageinterference canceling block, similar despreading, demodulation, datadecision, and respreading are carried out in the second stageinterference canceling block. For user 1, interference signal replicasS₂.sup.(1) +S₃.sup.(1) +. . . +S_(M).sup.(1) other than of user 1determined by the first stage interference canceling block aresubtracted from the reception signal S to produce a signal of improvedSIR, and on this signal, despreading, demodulation and data decision arecarried out. To other channels, similar processing is applied. That is,a signal, obtained by subtracting interference signal replicas in thefirst stage of channels other than own channel from the reception signalS, is subjected to respreading, demodulation, and data decision, andfrom the reproduction data, interference signal replicas S₁.sup.(2),S₂.sup.(2), . . . , S_(M).sup.(2) of individual channels in the secondstage interference canceling block are determined.

Accuracy of the interference signal replicas in the second stageinterference signal canceling block is improved compared with theinterference signal replicas in the previous stage. This is because datareproduction is made based on the signal obtained by subtraction ofinterference signal replicas in the previous stage. By repeating serialinterference cancellation in several stages, reliability of thereproduction data can be improved even further.

Under mobile communication environment, amplitude variation and phasevariation occur due to Rayleigh fading in association with variation inrelative positions between the mobile station and base station. In themulti-stage type interference canceler (serial interference canceler)shown in FIG. 1, it is necessary to estimate the phase and amplitudevariations in the process of generating the interference signalreplicas. The channel (phase; amplitude) estimation accuracy greatlyaffects the reception characteristics of the multi-stage typeinterference canceler, but realizability thereof is not described in theabove document. As a method in which estimation of transmission pathvariation under mobile communication environment is added to the serialinterference canceler of the above document, there is another document:Fukazawa et al., "Construction and characteristics of interferencecanceler according to transmission path estimation using a pilotsignal", Proceedings of the Electronic Information CommunicationSociety, Vol. J77-B-II No. 11, pp. 628-640, Nov. 1994.

FIGS. 2A and 2B are block diagrams showing a serial canceler shown inthis document. FIG. 3 shows the channel structure of the method.

In FIGS. 2A and 2B, the numeral 21 indicates a spreading code inputterminal, 22 is a first stage reproduction data output terminal of user1, 23 is a delay unit, 24 is a pilot channel transmission path variationestimator, 25 is an interference subtractor, 26 is a first stageinterference canceling block, 27 is a second stage interferencecanceling block, 28 is a matched filter, 29 is a transmission pathcompensator, 30 is a RAKE combiner, 31 is data decision block, 32 is asignal distributor, 33 is a transmission path variation adder, and 34 isa respreader.

This system, as shown in FIG. 3, is provided with a pilot channel havinga known transmission pattern parallel with the communication channel.Transmission path estimation is made based on the reception phase of thepilot channel. Further, amplitude/phase estimation of the receptionsignal of each path of each user is carried out based on thetransmission path estimation of the pilot channel. Still further, usingthe amplitude/phase estimation value, interference canceling of severalstages is carried out by the serial interference canceling block toreproduce data of each user. In this case, as in the previous document,individual paths are ranked in the decreasing order of the sum ofreception signal power. In the case of FIGS. 2A and 2B, the user 1reception signal power is assumed as to be the highest.

In the first stage interference canceling block, demodulation is firstcarried out on user 1. That is, each path of user 1 is despread by amatched filter 28, in a transmission path variation compensator 29, eachpath of user 1 is compensated for phase variation according to the phasevariation of each path estimated with respect to the pilot channel.Further, in the RAKE combiner 30, signals of the phase variationcompensated paths are phase synthesized by a reception complex envelopecurve of individual paths. The phase synthesized signal is decided bythe data decision block 31 to obtain reproduction data of user 1. Thedistributor 32 distributes the reproduction data replica according toweighting at the RAKE combining, the transmission path variation adder33 gives a phase variation of each path, and the respreader 34 makesrespreading by spreading code of each path to produce the interferencesignal replica S₁.sup.(1).

For user 2, the following processing is made. First, a delay unit 35delays the reception signal S. The interference subtractor 25 subtractsthe interference signal replica S₁.sup.(1) of user 1 from the delayedsignal. The first stage interference canceling block of user 2 carriesout despreading, phase compensation, RAKE combining, data decision, andproduction of interference signal replica for each path to the outputsignal of the interference subtractor 25. In this case, the input signalof the interference signal canceling block of user 2 is improved inreception SIR to the extent that the user 1 interference signal replicasare subtracted. Similarly, reproduction data is estimated for each userby the first stage interference canceling block up to user M to obtaininterference signal replicas.

The interference signal canceling block of second stage carries outsimilar processing using interference signal replicas S₁.sup.(1),S₂.sup.(1), . . . , S_(M).sup.(1) obtained by the interference signalcanceling block of the first stage. For example, the second stageinterference signal canceling block 27 (comprising the components 28-34of the first stage) of user 1 makes data demodulation by despreading thesignal obtained by subtracting the channel interference signal replicasother than own channel from the reception signal S delayed by delay unit23.

A difference of the prior art method from the method described in theprevious document is the following point. In the previous method, foruser 2, for example, interference signal replicas S₁.sup.(1) +S₃.sup.(1)+. . . +S_(M).sup.(1) in the foregoing stage are used as interferencesignal replicas of all paths. On the other hand, in the method of thisdocument, S₁.sup.(2) is used as an interference signal replica of user 1in the second stage. Compared with the estimated value S₁.sup.(1) in theforegoing stage, the estimated value S₁.sup.(2) in this stage is higherin reliability. Therefore, the accuracy of the desired wave signalobtained by subtracting the interference replicas and reliability ofdecision data obtained by demodulation are also improved.

However, in this method, a pilot channel is provided in parallel withthe communication channel for each user, and a channel estimated in thepilot channel is used in each stage of interference canceling block. Inthis case, since channel estimation in the pilot channel is carried outindependent of the interference canceling loop, to estimate channel(phase, amplitude) variation in high accuracy, it has been necessary tomake averaging over a very long time (using many pilot symbols). Foraveraging using such numerous pilot symbols, it is assumed that channelestimation values in this period be approximately constant, therefore,it is limited to be applied to an environment of fast channel variation(high fading frequency). When fading is fast, averaging is possible onlyin a range where the values can be regarded as constant, it is thereforeimpossible to obtain a sufficient channel estimation accuracy if thenumber of averaging symbols is small.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a CDMA demodulatingapparatus, which can improve reliability of reproduction data in a lowSIR environment with a number of simultaneous users.

In a first aspect of the present invention, there is provided a CDMA(Code Division Multiple Access) demodulating apparatus for use in a CDMAcommunication system that performs spreading information data by aspreading code faster than an information rate to a wideband signal andthe wideband signal is transmitted to achieve multiple accesstransmission, wherein a pilot symbol of know pattern is received toestimate channel variation, individual reception signals receivedthrough a plurality of channels are compensated by the estimated channelvariation, and the compensated reception signal is demodulated toreproduce the information data, comprising:

a correlation detector using a spreading code as a spreading codereplica synchronized with a reception timing of each path of each of thechannel for correlation detection of the spreading code replica with thereception signal of each path;

a received level detector for determining a sum of a reception power ofa corresponding path of the correlation detector and detecting a desiredwave reception signal level;

a channel ranking unit for controlling order of demodulation of the useraccording to the reception signal level of each user detected by thereceived level detector; and

an interference canceler of a plurality of stages for makinginterference canceling according to a control signal outputted from thechannel ranking unit, in each of the plurality of stages, makingestimation of channel variation using the pilot symbol on each channel,compensating the reception signal of the channel by the estimatedchannel variation, and respreading the compensated reception signal toproduce an interference signal replica.

In the CDMA demodulating apparatus, the interference canceler of an i'th(i being an integer of 2 or more) stage of the plurality of stages mayuse the interference signal replica of each user estimated by theinterference canceler of the (i-1)th stage as an input to supply theinterference signal replica of each user estimated by the interferencecanceler of the i'th stage to the interference canceler of a (i+1)'thstage.

In the CDMA demodulating apparatus, each of the interference canceler ofeach stage may comprise a sub-interference canceler for each user forproducing the interference signal replica, the sub-interference cancelerof a k'th (k=any of 1, 2, . . . , M ) user of the interference cancelerof the i'th stage comprising:

an interference subtractor for subtracting interference signal replicasin the interference canceler of the i'th stage as interference signalreplicas of first, second . . . and (k-1)th users from the receptionsignal, subtracting interference signal replicas in the interferencecanceler of an (i-i)'th stage as interference replicas of (k+1)'th, . .. (M-1)'th and M'th users from the reception signal;

a channel variation estimator for estimating a channel variation of thepilot symbol in the output signal of the interference subtractor foreach path, and estimating the channel variation by interpolating thechannel variation of the estimated pilot symbol into a position of eachsymbol of the information data in the output signal of the interferencesubtractor;

a channel variation compensator for compensating the reception signalfor the channel variation estimated for each path by the channelvariation estimator;

a RAKE combiner for synthesizing the reception signal of each pathoutputted from the channel variation compensator;

a data decision block for deciding the output signal of the RAKEcombiner;

a channel variation adder for adding a channel variation obtained as anoutput of the channel variation estimator to the decision data outputtedfrom the data decision block;

a respreader for spreading a signal of each path outputted from thechannel variation adder by a spreading code synchronized with receptiontiming of each path; and

an adder for adding the output of the respreader to produce aninterference signal replica of the k'th user.

In the CDMA demodulating apparatus, the correlation detector maycomprise a plurality of matched filters.

In the CDMA demodulating apparatus, the correlation detector maycomprise a plurality of sliding correlators.

In the CDMA demodulating apparatus, the pilot symbol may be insertedperiodically between the information data.

In the CDMA demodulating apparatus, the interference canceler of eachstage may comprise one unit of the sub-interference canceler, andmemories for storing interference replicas of individual users ofindividual stages, using the sub-interference canceler in time division.

In the CDMA demodulating apparatus, the interference canceler may use ablock as a processing unit a block of constant time including at leasttwo adjacent pilot signal sections, and the sub-interference cancelermay further comprise an extrapolating unit for an information symboloutside the pilot signal section for extrapolating the pilot symbolclosest to the information symbol to determine channel variation of theinformation symbol.

In the CDMA demodulating apparatus, a subtractor for subtracting aninterference signal replica other than of a j'th path of the k'thcommunicator in an (i-1)'th stage from the output signal of theinterference subtractor may be provided at the input side of thecorrelation detector of the j'th (j being 1 to a path number Lk of RAKEcombining) of the k'th user of the i'th (i being an integer of 2 ormore) stage interference canceler.

In the CDMA demodulating apparatus, the sub-interference canceler mayfurther comprise:

a reception signal power detector for detecting a power of the receptionsignal of each path after despreading outputted from the correlationdetector;

an adder for adding the reception signal powers of the individual paths;

an amplitude converter for detecting amplitudes of in-phase componentand quadrature component from the output of the adder;

an averaging unit for averaging the output signal of the amplitudeconverter; and

a multiplier for multiplying the decision data by an output of theaveraging unit.

In the CDMA demodulating apparatus, the interference canceler of thefirst stage may comprise a decorrelation filter for using a signal ofeach path of K'th (K being an integer of 2 to spreading factor PG) userfrom the higher reception signal level to obtain a despread outputvector which is interference removed each other;

and a coherent detector/interference generator for estimatingtransmission data of K users outputted from the decorrelation filter andgenerating an estimated interference amount of each user, wherein

the interference canceler uses the interference signal replica outputtedfrom the coherent detector/interference generator as interference signalreplicas of the K users to produce individual interference signalsreplicas of the remaining (M-K) users.

In the CDMA demodulating apparatus, the interference canceler of i'th (ibeing an integer of 2 or more) stage of the plurality of stages may usethe interference signal replica of each user estimated by theinterference canceler of the (i-1)'th stage as an input and supply theinterference canceler of (i+1)'th stage with an estimated interferenceamount of each user estimated by the interference canceler of the i'thstage.

In the CDMA demodulating apparatus, the first stage interferencecanceler may comprise a sub-interference canceler for producing theestimated interference amount for each user of (K+1)'th user and after,and the sub-interference canceler of a k'th (k=(K+1), (K+2), . . . , orM) user may comprise:

an interference subtractor for subtracting interference signal replicasin the interference canceler of the i'th stage as interference signalreplicas as estimated interference amounts of first, second . . . andK'th th users from the reception signal, and subtracting interferencesignal replicas in the interference canceler of the first stage asinterference replicas of (K+1), . . . (k-1)'th users from the receptionsignal;

a channel variation estimator for estimating a channel variation of thepilot symbol in the output signal of the interference subtractor foreach path, and estimating the channel variation of each informationsymbol by interpolating the channel variation of the estimated pilotsymbol into a position of each symbol of the information data in theoutput signal of the interference subtractor;

a channel variation compensator for compensating the reception signalfor the channel variation estimated for each path by the channelvariation estimator;

a RAKE combiner for synthesizing the reception signal of each pathoutputted from the channel variation compensator;

a data decision block for deciding the output signal of the RAKEcombiner;

a channel variation adder for adding a channel variation obtained as anoutput of the channel variation estimator to the decision data outputtedfrom the data decision block;

a respreader for spreading a signal of each path outputted from thechannel variation adder by a spreading code synchronized with receptiontiming of each path; and

an adder for adding the output of the respreader to produce aninterference signal replica of the k'th user.

Each of the interference canceler of the second stage and after maycomprise a sub-interference canceler for each user for producing theinterference signal replica , the sub-interference canceler of a k'th(k=any of 1, 2, . . . , M) user of the interference canceler of the i'thstage comprising:

an interference subtractor for subtracting interference signal replicasin the interference canceler of the i'th stage as interference signalreplicas of first, second . . . and (k-1)th users from the receptionsignal, and subtracting interference signal replicas in the interferencecanceler of an (i-1)'th stage as interference replicas of (k+1)'th, . .. (M-1)'th and M'th users from the reception signal;

a channel variation estimator for estimating a channel variation of thepilot symbol in the output signal of the interference subtractor foreach path, and estimating the channel variation of the informationsymbol by interpolating the channel variation of the estimated pilotsymbol into a position of each symbol of the information data in theoutput signal of the interference subtractor;

a channel variation compensator for compensating the reception signalfor the channel variation estimated for each path by the channelvariation estimator;

a RAKE combiner for synthesizing the reception signal of each pathoutputted from the channel variation compensator;

a data decision block for deciding the output signal of the RAKEcombiner;

a channel variation adder for adding a channel variation obtained as anoutput of the channel variation estimator to the decision data outputtedfrom the data decision block;

a respreader for spreading a signal of each path outputted from thechannel variation adder by a spreading code synchronized with receptiontiming of each path; and

an adder for adding the output of the respreader to produce aninterference signal replica of the k'th user.

In the CDMA demodulating apparatus, the correlation detector maycomprise a plurality of matched filters.

In the CDMA demodulating apparatus, the correlation detector maycomprise a plurality of sliding correlators.

In the CDMA demodulating apparatus, the pilot symbol may be insertedperiodically between the information data.

In the CDMA demodulating apparatus, the interference canceler of eachstage may comprise one unit of the sub-interference canceler, andmemories for storing interference replicas of individual users ofindividual stages, using the sub-interference canceler in time division.

In the CDMA demodulating apparatus, the coherent detector/interferencegenerator may comprise:

a channel variation estimator for estimating a channel variation of thepilot symbol in the output signal of the interference subtractor foreach path, and estimating the channel variation of each informationsymbol by interpolating the channel variation of the estimated pilotsymbol into a position of each symbol of the information data in theoutput signal of the interference subtractor;

a channel variation compensator for compensating the reception signalfor the channel variation estimated for each path by the channelvariation estimator;

a RAKE combiner for synthesizing the reception signal of each pathoutputted from the channel variation compensator;

a data decision block for deciding the output signal of the RAKEcombiner;

a channel variation adder for adding a channel variation obtained as anoutput of the channel variation estimator to the decision data outputtedfrom the data decision block;

a respreader for spreading a signal of each path outputted from thechannel variation adder by a spreading code synchronized with receptiontiming of each path; and

an adder for adding the output of the respreader to produce aninterference signal replica of the k'th user.

The CDMA demodulating apparatus may further comprise:

an SIR measuring unit for measuring an SIR of the output of thecorrelation detector;

a reception quality measuring unit for measuring a reception quality ofthe output signal of the interference canceler;

a target SIR setting unit for setting a target SIR according to themeasured reception quality and a required reception quality; and

a transmission power control signal generator for comparing SIRoutputted from the SIR measuring unit with the target SIR.

In the CDMA demodulating apparatus, the SIR setting unit may set aninitial value of the target SIR according to the number of simultaneouscommunicators.

In the CDMA demodulating apparatus, the reception quality measuring unitmay comprise an error ratio measuring unit for measuring a frame errorratio, and means for comparing the frame error ratio with apredetermined threshold value of frame error ratio to decide thereception quality.

In the CDMA demodulating apparatus, the reception quality measuring unitmay comprise an error ratio measuring unit for measuring a bit errorratio of the pilot symbol, and means for comparing the bit error ratiowith a predetermined threshold value of bit error ratio to decide thereception quality.

In the CDMA demodulating apparatus, the correlation detector may be amatched filter.

In the CDMA demodulating apparatus, the interference canceler maycomprise a reception vector generator for generating a reception vectorcomprising despread signal of each path for each channel from the outputsignal of the matched filter, a cross-correlation inverse matrixgenerator for calculating cross-correlation of all spreading codes otherthan the spreading code of own channel and receiver input to produce aninverse matrix of a matrix comprising cross-correlation, and a matrixvector multiplier for compensating the reception vector by the inversematrix to remove cross-correlation between individual reception vectorsthereby removing interference.

Secondly, according to the present invention, there is provided a CDMA(Code Division Multiple Access) demodulating apparatus for use in a CDMAsystem that performs multiple access transmission by transmitting aspread signal, the spread signal being generated by spreadinginformation data into a wideband signal with a spreading code whose rateis higher than an information rate, wherein a pilot symbol of a knownpattern to estimate a channel variation, each reception signal receivedthrough a plurality of channels is compensated by the estimated channelvariation, and the compensated reception signal is demodulated toreproduce the information data, the demodulating apparatus comprising:

a correlation detector, using a spreading code in phase with receptiontiming of each path of each channel, for detecting correlation of thespreading code with the reception signal of each path;

a received level detector for determining a sum of a reception power ofa corresponding path of the correlation detector and detecting a desiredwave reception signal level;

a channel ranking unit for controlling order of demodulation of the useraccording to the reception signal level of each user detected by thereceived level detector;

an interference canceler of a plurality of stages for despreading thereception signal for individual users according to an order determinedby the control signal outputted from the channel ranking unit,respreading the despread signal, and subtracting an interference signalreplica of other users obtained by respreading from the reception signalof the corresponding user; and

a pilot interpolation/coherent detector for estimating a channelvariation using the pilot symbol in the signal after subtracting by aninterference amount of other users in the interference canceler of thelast stage in the plurality of stages, compensating the information datausing the estimated channel variation to perform absolutesynchronization detection of the compensated information data.

In the CDMA demodulating apparatus, an i'th (i being an integer of 2 ormore) stage interference canceler may use the interference signalreplica of each user estimated in the (i-1)'th stage interferencecanceler as an input to supply the interference signal replica estimatedin the i'th stage interference canceler to the (i+1)'th stageinterference canceler.

In the CDMA demodulating apparatus, each interference canceler of eachof the stages comprises a sub-interference canceler for each user forproducing the interference signal replica, the sub-interference cancelerof a k'th (k=1, 2, . . . , or M) user of the i'th stage interferencecanceler comprising:

an interference subtractor for subtracting interference signal replicasin the interference canceler of the i'th stage as interference signalreplicas of first, second . . . and (k-1)th users from the receptionsignal, subtracting interference signal replicas in the interferencecanceler of an (i-1)'th stage as interference replicas of (k+1)'th, . .. (M-1)'th and M'th users from the reception signal;

a matched filter for making correlation detection between the outputsignal of the interference subtractor and a spreading code replica inphase with reception timing of each path to obtain a despread signal ofeach path; and

a respreading/combiner unit for spreading the despread signal of eachpath with a spreading code in phase with the reception timing of eachpath, estimating an interference signal replica of the path of eachuser, and adding the estimated interference signal replica to produce aninterference signal replica of each user.

In the CDMA demodulating apparatus, the pilot symbol may be insertedperiodically between the information data.

In the CDMA demodulating apparatus, the interference canceler of eachstage may comprise one unit of the sub-interference canceler, andmemories for storing interference replicas of individual users ofindividual stages, using the sub-interference canceler in time division.

In the present invention, channel variation is estimated using a pilotsignal in each channel of each stage. In other words, a channelvariation estimator using the pilot signal is included in theinterference canceler loop of each channel of each stage. As a result,accuracy of interference signal replica is successively improved inindividual stages of the interference canceler, thereby improving theestimated accuracy of each channel. Therefore, the interferencecanceling effect is improved when there are a large number of users.

Further, for some of users of first stage with low SIR, interference isremoved by a decorrelation filter to improve the SIR, and thendemodulation is made, thereby improving the accuracy of decision dataand interference signal replica. Since subsequent interference cancelersperform interference canceling using the decision data and interferencesignal replicas, estimation accuracy of channel variation is improved.

For first several users of high ranking with low SIR, interferencereduction is made using a decorrelator, and channel estimation iscarried out on the interference reduced signal using a pilot symbol,thereby improving the estimation accuracy on the several users.

Yet further, at the receiving side, the communication quality ismeasured at the output side of the multi-user type interferencecanceler, the reception quality information is fed back to the SIRthreshold value of SIR measurement, and a constant SIR type closed looptransmission power control is performed by the matched filter outputsignal, thereby achieving transmission power control signal based on SIRof interference reduced signal without increasing delay of control.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of showing the structure of a multi-stageinterference canceler in a prior art CDMA demodulating apparatus;

FIGS. 2A and 2B are block diagrams showing the structure of anotherprior art multi-stage interference canceler.

FIG. 3 is a schematic view showing a prior art channel arrangement usedin the apparatus of FIGS. 2A and 2B.

FIG. 4 is a block diagram showing the entire structure of a firstembodiment of the CDMA demodulating apparatus according to the presentinvention;

FIGS. 5A and 5B are block diagrams showing a multi-stage interferencecanceler for the CDMA demodulating apparatus shown in FIG. 4.

FIG. 6 is a schematic view showing the frame arrangement used in thefirst embodiment;

FIG. 7 is a vector diagram for illustrating an information data phaseerror compensation method using a pilot signal in the first embodiment;

FIGS. 8 and 9 are graphs showing an effect of the multi-stageinterference canceler in the first embodiment;

FIG. 10 is a block diagram showing an interference canceler used in asecond embodiment of the CDMA demodulating apparatus according to thepresent invention;

FIG. 11 is a block diagram showing the structure of a channel variationestimator and a channel variation compensator for producing aninterference replica of each user in an interference canceler of a thirdembodiment of the CDMA demodulating apparatus according to the presentinvention;

FIG. 12 is a schematic view for illustrating an interference replicagenerating method in the third embodiment;

FIG. 13 is a vector diagram for illustrating a channel variationestimation method for generating an interference replica in the thirdembodiment;

FIG. 14 is a block diagram showing an ICU (interference canceling unit)of a k'th user of the multi-stage interference canceler after the secondstage in a fourth embodiment of the CDMA demodulating apparatusaccording to the present invention;

FIG. 15 is a block diagram showing an ICU of the k'th user in a fifthembodiment of the CDMA demodulating apparatus according to the presentinvention;

FIGS. 16A and 16B are block diagrams showing the first stageinterference canceler in a sixth embodiment of the CDMA demodulatingapparatus according to the present invention;

FIGS. 17A and 17B are block diagram s showing the multi-stageinterference canceler in a seventh embodiment of the CDMA demodulatingapparatus according to the present invention;

FIGS. 18A and 18B are block diagrams showing the entire construction ofan eighth embodiment of the CDMA demodulating apparatus according to thepresent invention;

FIGS. 19A and 19B are block diagrams showing the multi-stageinterference canceler in the eighth embodiment, in which a portionsurrounded by the broken line in FIG. 19B is a modification example ofthe eighth embodiment;

FIG. 20 is a block diagram showing the multi-stage interference cancelerand a pilot interpolation/RAKE combining coherent detector of a ninthembodiment of the CDMA demodulating apparatus according to the presentinvention;

FIG. 21 is a graph showing an error of closed loop transmission powercontrol against a fading rate;

FIG. 22 is a block diagram showing an embodiment in which transmissionpower control is applied to the CDMA demodulating apparatus according tothe present invention;

FIGS. 23A and 23B are block diagrams showing the construction of areception quality measuring unit of FIG. 22;

FIG. 24 is a schematic view comparing reception power in a matchedfilter output in FIG. 22 with reception power in an interferencecanceler output;

FIG. 25 is a block diagram showing another embodiment in whichtransmission power control is applied to the CDMA demodulating apparatusaccording to the present invention;

FIG. 26 is a block diagram showing a further embodiment in whichtransmission power control is applied to the CDMA demodulating apparatusaccording to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will now be described in detailwith reference to the accompanying drawings.

Embodiment 1

FIG. 4 is a block diagram showing the entire construction of the firstembodiment of the CDMA demodulating apparatus according to the presentinvention, FIGS. 5A and 5B are block diagrams showing the constructionof interference canceling blocks of the first stage and the second stageof the CDMA demodulating apparatus, and FIG. 6 is a schematic viewshowing the frame arrangement of the CDMA demodulating apparatus towhich the present invention is applied.

The frame of the system to which the present invention is applied, asshown in FIG. 6, has a structure in which pilot signals of a knownpattern are inserted periodically between information signals in unitsof several symbols.

A receiver of the system comprises, as shown in FIG. 4, matched filters103 and received level detectors 104 provided corresponding to channels1-N, a channel ranking unit 105, and interference canceling blocks106-108 of first-H'th stages. The matched filter 103, in each path ofeach channel, performs correlation detection of the spreading codereplica with the reception signal using the spreading code in phase withthe reception timing as a spreading code replica. The received leveldetector 104 makes a sum of reception power of individual pathsoutputted from the matched filters 103 to detect the received level of adesired wave. The channel ranking unit 105 outputs a channel rankinginformation for controlling the order of demodulation of users of thereceiver input according to the reception signal level of each user. Theinterference canceling blocks 106-108 perform demodulation in the orderof higher received level according to the channel ranking information,and output new interference signal replicas of individual users usinginterference signal replicas estimated by the interference cancelingblock of the previous stage.

FIGS. 5A and 5B individually show the constructions of the interferencecanceling blocks 106 and 107.

A received spread signal S supplied to an input end 201 of theinterference canceling block 106 is fed to delay units 202, 203(203-2-203-M) and an interference canceling unit 210-1 (hereinafterreferred to as ICU). Output of the delay unit 202 is fed to theinterference canceling block 107 of the second stage. Further, output ofeach delay unit 203 is fed to each interference subtractor 204(204-2-204-M). These delay units 203 are for synchronizing processingtiming. An interference subtractor 204-k of the k'th user (k=2, . . . ,or M) subtracts interference signal replicas in the correspondinginterference canceling block of the first, 2nd, . . . (k-1)'th users andinterference signal replicas in the interference canceling block of theprevious stage of (k-1)'th . . . , (M-1), M'th users from the inputsignal.

The ICU are provided in the number of users×number of stages. Thestructure is illustrated using the ICU 210-1 of user 1 of the firststage as an example. The ICU 210-1 comprises a matched filter 211, apilot symbol channel variation estimator (herein after referred to asPCHE) 212 and a channel variation compensator 213, a RAKE combiner 214,and a data decision block 215 provided in each of multiple paths, achannel variation adding unit 216 and a respreader 217 provided in eachpath, and an adder 218, and output of the adder 218 (channel variationestimation value) is outputted from an output terminal 219.

The matched filter 211 makes cross-correlation of a received spreadsignal with a spreading code for each path, and outputs a despreadsignal. The PCHE 212 estimates a variation in the transmission path ofeach path of each symbol in the despread signal. That is, for each path,the transmission variation estimated by the pilot symbol is interpolatedinto the information position in the section to estimate thetransmission path variation in each information symbol. The channelvariation compensator 213 compensate an estimated phase variation foreach path. The RAKE combiner 214 makes weighted combination of outputsignal of each channel variation compensator 213 according to themagnitude of reception power of each path. The data decision block 215decides output signal of the RAKE combiner and outputs a decision data.The channel variation adder gives a phase variation outputted from PCHE212 to the signal of each path outputted from the data decision block215. The respreader 217 respreads the signal of each path outputted fromthe channel variation adding unit 216 with a spreading code in phasewith the reception timing of each path. The adder 218 calculates the sumof the estimated reception signal of each path of this user to produce areception signal replica S₁.sup.(1) of the user. Since the receptionsignal replica S₁.sup.(1) is an interference to other channels, it canbe referred to as an interference signal replica. The interferencesignal replica S¹.sup.(1) is fed to the delay unit 204-2 of user 2, andsubtracted from the received spread signal S delayed by the delay unit203-2. Therefore, in the ICU 210-2 of the second user, interferencecanceling is made on an interference-reduced signal. Other ICUs 210 ofthis stage have the similar construction. Further, other interferencecanceling blocks 107 and 108 are also similar in construction.

Operation of the present embodiment will be described. The matchedfilter 103 despread the receiver input signal using the correspondingspreading code of each path of each user as a replica. The receivedlevel detector 104 determines a reception signal power for each user byadding the matched filter correlation output value of multiple paths tobe synthesized for each user. The channel ranking unit 105 makes rankingin the order of higher reception signal power level and outputs channelranking information.

The serial canceling blocks 106-108 carry out demodulation successivelyfrom the user of higher ranking. Operation of the interference cancelingblock 106 of the first stage is as follows.

The ICU 210-1 produces the interference signal replica S₁.sup.(1) ofuser 1. First, the matched filter 211 despreads the received spreadsignal S for each path. The PCHE 210 interpolates a reception phase inthe pilot symbol for each information bit between pilot symbols shown inFIG. 6, to determine a transmission path phase variation of eachinformation symbol.

FIG. 7 shows a transmission path variation estimation method ofinformation symbol by interpolation of pilot symbols. The axis ofabscissas of FIG. 7 indicates magnitudes of in-phase components of pilotsymbol and information symbol, and the axis of ordinates indicatesmagnitudes of these quadrature components. Pi and Pi+1 indicatereception phase vectors of the pilot symbol determined by averaging ineach pilot symbol section. A broken line L1 is a straight line obtainedby linear interpolation of the reception phase vectors Pi and Pi+1 inthe information symbol section. Vectors S1, S2, . . . indicate receptionphase vectors of each information symbol estimated by the interpolation.A curve C1 indicates a locus of actual reception phase vectors of eachsymbol in association with the transmission path variation. As shown inFIG. 7, the reception phase vector of the information symbol can beestimated by linear interpolation of reception phase vectors in eachpilot symbol section to the position of each information symbol in thesection. In the present embodiment, such estimation of phase variationby pilot symbol is performed for each path of each user of each stage.The insertion interval of the pilot symbols is determined to follow thephase variation of the transmission path.

The channel variation compensator 213 makes phase compensation of theinformation symbol using the resulting channel phase variationestimation value. The RAKE combiner 214 RAKE synthesizesphase-compensated signals of each path using the reception power of eachpath as weighting. The data decision block 215 identifies and decidesthe RAKE synthesized signal to produce a reproduction data replica. Thechannel variation adding unit 216 adds an estimated phase variation ofeach path to the decided data. The respreader 217 respreads the outputof the channel variation adding unit 216 using a spreading code in phasewith the reception timing of each path to obtain a interference signalreplica of each path. The adder 218 determines the sum of interferencesignal replicas of individual paths to obtain the interference signalreplica S₁.sup.(1) of user 1.

Next, processing on user 2 will be described. The interferencesubtractor 204-2 subtracts the interference signal replica S₁.sup.(1) ofuser 1 from the received spread signal S. The ICU 210-2 estimates aninterference amount S₂.sup.(1) of user 2 same as in ICU 210. In thiscase, input signal to the ICU 210-2 of user 2 is improved in SIR(Signal-to-Interference ratio) as compared with the received spreadsignal S. This is because the interference signal replica S₁.sup.(1) issubtracted from the reception signal S. Similarly, since the inputsignal to the ICU of a k'th user is subtracted by interference signalreplicas of first to (k-1)'th users, the SIR can be successivelyenhanced. Thereafter, on each user to M'th user, data demodulation isperformed on the signal subtracted by the sum of interference signalreplicas up to the immediately previous user.

The second stage interference canceling block 107 carries outdemodulation successively from user 1 as in the first stage interferencecanceling block 106. Specifically, the ICU 230-1 of user 1 determinesthe interference signal replica of user 1 on the signal subtracted bythe sum of interference signal replicas of other users in the firststage, S₂.sup.(1) +S₃.sup.(1) +. . . S_(M).sup.(1) from a receptionsignal Sd, of which delayed processing is considered, as in the ICU210-1.

The ICU 230-2 of user 2 of the second stage also makes the sameprocessing on the signal subtracted by the sum of the first userinterference signal replica obtained in the second stage and theinterference signal replicas from the third user to M'th user,S₁.sup.(2) +S₃.sup.(1) + . . . +S_(M).sup.(1), from the reception signalSd to determine the interference replica of the 2nd user. Further, theICU 230-M of M'th user also makes the same processing on the signalsubtracted by the sum of interference signal replicas of other usersestimated in the second stage, S₁.sup.(2) +S₂.sup.(2) + . . .+S_(M-1).sup.(2), from the reception signal Sd to determine theinterference signal replica of M'th user.

In other words, k'th user uses the interference signal replica in thecorresponding stage on a user of higher ranking (higher in receptionsignal level) then own, and on the users of lower ranking than own, usesthe interference signal replicas produced in the interference cancelingblock of the previous stage to calculate the interference signalreplica.

The point of the present embodiment differing from the prior art is thatphase estimation of each path is made for each user of each stage. Bythis method, the accuracy of the interference signal replica of eachuser is improved every time one stage of the interference cancelingblock is passed. As a result, estimation error subtracted byinterference signal replicas of other users from the reception signal isreduced, and estimation accuracy of phase variation is also improved.

In the present embodiment, the matched filter is used as despreadingmeans, however, alternatively, sliding correlators of the number ofpaths can be used to obtain the same characteristics.

FIG. 8 is a graph showing an average bit error ratio in CDMAdemodulating apparatus of the present invention compared with the priorart apparatus. In this graph, the axis of abscissas indicates Eb/No(energy per bit to noise spectral density), and the axis of ordinatesindicates the average bit error ratio. In the prior art apparatus, asshown in FIG. 7, that the pilot symbol obtained by despreading isinterpolated in the information symbol section to estimate the channelvariation is the same as in the present invention. However, whereas inthe present invention, channel estimation on each path of each user issuccessively carried out for each stage of the interference cancelingblock, the prior art apparatus differs in that it uses the receptionvectors obtained in each pilot symbol section of each user commonly forall stages of the interference canceling block.

As can be seen from the graph shown in FIG. 8, the improvement in theerror ratio is almost the highest when the interference canceling blockis three stages, but almost no increase in effect is noted even if thenumber of stages is further increased. Further, where Eb/No is 10 dB,the apparatus of the present invention can reduce the error ratio nearlyone figure compared with the prior art apparatus.

FIG. 9 is a graph comparing the average bit error ratio with a weightedaverage between the present pilot section and the previous pilot sectionto make phase estimation of pilot symbol. In the figure, α and (1-α)indicate weighting and black circles indicate the error ratio of thepresent invention. As can be seen from the figure, for Eb/No in thevicinity of 10 dB, the error ratio of the present invention is about 1/6the weighted averaging.

Embodiment 2

FIG. 10 is a block diagram showing a second embodiment of theinterference canceling block of the CDMA demodulating apparatusaccording to the present invention. A difference of this embodiment fromthe first embodiment is that processing of all stages for M users isperformed by a single ICU. That is, the hardware is simplified byrepeatedly using a single ICU in time division.

In FIG. 10, the received spread signal S inputted to an input terminal301 is fed to a memory 303. The memory 303 functions as a delay unitunder control of a user control signal (channel ranking signal) suppliedfrom the channel ranking unit 105. That is, it corresponds to the delayunits 202, 203 and 223 in FIG. 5A. Further, an interference subtractor304 corresponds to the interference subtractor 204 and 224, whichsubtracts the interference signal replica read from an interferencesignal replica memory 305 from the spread signal S read from the memory303. The ICU 310 corresponds to the ICU 210 of FIG. 5A and the ICU 230of FIG. 5B, which performs channel estimation, RAKE combining, andinterference signal replica production on the output of the interferencesubtractor 304 to output a new interference signal replica. Thus, theICU 310 successively updates the interference signal replica of eachpath of each user, and writes the resulting interference signal replicainto the interference signal replica memory 305.

Embodiment 3

FIG. 11 is a block diagram showing the construction of a matched filterin ICU, a PCHE (pilot symbol channel variation estimator) and a channelvariation compensator in a third embodiment of the CDMA demodulatingapparatus of the present invention. The principle will be describedbefore describing the third embodiment in detail.

In a cellular communication system, in a downward channel from a basestation to a mobile station, transmission timing of each user issynchronized with each other. However, since transmission delay differsin an upward channel responding to it, information symbol timing andspreading code chip timing are asynchronous.

FIG. 12 shows a frame-arrangement of each user in an asynchronouschannel. As shown in the figure, on the pilot symbol of user X, there isan interference of the information symbol in the previous pilot block ofuser Y. This is because in the multi-stage interference canceler, anestimation interference replica is produced in a unit of chip.Therefore, multi-stage interference canceling performed in a unit of 1pilot block is required to be performed in a unit of time includinginformation symbols before and after the pilot block. That is, it isnecessary to produce an estimation interference replica in a unit ofinterference canceling time TA including the information symbols beforeand after, rather than pilot block time TB as shown in FIG. 12.Therefore, processing such as channel ranking by an average value ofreception signal level, production of estimated interference replica,and the like must be performed in every processing time TA.

FIG. 13 is a vector diagram showing the principle of channel estimationfor the production of interference replica in an asynchronous channel. Adifference between the processing in FIGS. 7 and 13 is that the channelvariation is estimated by extrapolating a reception envelope line of thepilot symbol for several symbols outside a pilot symbol Pi. Since thenumber of the outside symbols is several symbols even consideringtransmission delay, no substantial error is produced even if the channelvariation estimation value of the pilot symbol is adopted as a channelestimation value of the information symbol outside the pilot symbol. Byusing these estimation values, the spread signal replica of theinformation symbol outside the pilot symbol can be produced. Further,for an information symbol sandwiched between two pilot symbols,variation is estimated by interpolating the pilot symbols in theinformation symbol section, as in FIG. 7, to produce the spread signalreplica of the information symbol. By subtracting these spread signalreplicas from the reception signal S to form the multi-user interferencecanceler even in an upward asynchronous channel. With this method, ifonly the reception signal in 1 pilot block time TB is stored in thememory, interference replicas can be produced in the range of longerprocessing time TA, thereby achieving an efficient multi-userinterference canceler.

Reverting back to FIG. 11, the construction of the PCHE and channelvariation compensator in the ICU of the present embodiment will bedescribed. Other construction is the same as in FIG. 5A.

In FIG. 11, the received spread signal applied to an input terminal 201is written in a reception signal memory 403. The memory 403 stores thereception signal in 1 pilot block time TB in FIG. 12. The storedreception signal is fed and despread in a matched filter 411. Thedespread signal is fed to a delay unit 413, a channel estimator 415, anda pilot frame synchronizer 419.

The channel estimator 415 extracts a pilot symbol of known pattern fromthe despread signal, which is compared with the pilot symbol suppliedfrom a pilot signal generator 417 to estimate the phase variation. Inthis case, the pilot symbol generation phase of the pilot signalgenerator 417 is controlled by a signal from the pilot framesynchronizer 419.

The phase variation estimated by the channel estimator 415 is convertedto a signal and fed to an interpolator 421 and an extrapolator 423. Foran information symbol inside the pilot block, the estimation valueestimated in the pilot section of both sides into the position of eachinformation symbol to estimate channel variation of each informationsymbol. On the other hand, for an information symbol outside the pilotblock, the estimation channel variation in the pilot section closest tothe information symbol is determined as a channel variation estimationvalue. As described above, the number of information symbols, evenconsidering transmission delay in a cellular system with a cell radiusof several km, is only a few. These channel variation estimation valuesare fed to a fading distortion compensator 425, multiplied to thedespread signal passed through the delay unit 413 to compensate for thechannel variation.

The processing is performed on each path of this user, and the channelvariation compensated despread signal of each path is fed to a RAKEcombiner 430. The RAKE synthesized signal is decided by a data decisionblock 440.

With the present embodiment, even in an upward asynchronous channel,multi-stage interference canceling is possible by block processing in aunit of constant time. In the present embodiment, since it is notnecessary to communicate interference replica information betweenblocks, the apparatus can be simplified.

Embodiment 4

FIG. 14 is a block diagram showing the ICU of the interference cancelerafter the second stage of a fourth embodiment of the CDMA demodulatingapparatus according to the present invention. The present inventioneliminates interference replicas due to multipath signals of ownchannel.

In mobile communication environment, multipath transmission paths areformed due to reflection from buildings and ground. The multipath signalof own channel, as in the signals from other users, also producescross-correlation at despreading causing interference. As in theabove-described embodiments, in an arrangement where channel estimationis successively performed for each stage using pilot symbols, the inputsignals of ICU of the stages after the second stage include interferencereplicas due to multipath signals of own channel.

In a wideband DS-CDMA of high-speed chip rate, due to its low timeresolution, the reception signal can be separated to a number ofmultipath signals, and a RAKE combining function is effective. However,in the RAKE combining, the signal power per 1 path of multipath isreduced, interference from multipath signals of own channel becomes notnegligible. Therefore, in the multi-stage interference canceler, it isnecessary to use the signal subtracted not only by interference replicasof other users but also by interference replicas due to multipathsignals of own channel as an ICU input signal to improve SIR evenfurther.

FIG. 14 shows the ICU of k'th user of i'th stage (i being an integer of2 or more) of the CDMA demodulating apparatus which is achieved undersuch a concept.

Differences of ICU 510-k from the ICU 210 in the first embodiment shownin FIG. 5A are as follows.

(1) Interference replica eliminators 505 (505-1-505-Lk) are newlyprovided. The interference replica eliminators 505 are to eliminateinterference replicas due to multipath waves of own channel.

An interference subtractor 504-k of FIG. 14 corresponds to theinterference subtractor 224 of FIG. 5B, which subtracts interferencereplicas of other users from received spread signal S₂ (delayed receivedspread signal S) supplied to an input terminal 501. That is, theinterference subtractor 504-k, for users from the first user to (k-1)'thusers before itself, subtracts the interference replicas obtained in thepresent stage i from the received spread signal, and for users from(k+1)'th to M'th user after itself, subtracts the interference replicasobtained in the immediately prior (i-1)'th from the received spreadsignal. A received spread signal S₃ subtracted by interference replicasof other users is fed to the interference replica eliminators 505.

The interference replica eliminators 505 eliminate by subtractinginterference replicas of other multipath obtained in the immediatelyprior (i-1)'th stage from the received spread signal S₃. For example,the interference replica eliminator 505-1 subtracts all multipathinterference replicas after the second multipath obtained in theprevious (i-1)'th stage from the received spread signal S₃. In general,considering Li'th multipath wave of k'th user, interference replicasother than Li of k'th user estimated by the previous stage ICU aresubtracted from the received spread signal S3. The thus obtainedreceived spread signal is fed to the matched filter 211 providedcorresponding to each path, and thereafter subjected to the sameprocessing as in the first embodiment, and respread by the respreader217. In FIG. 14, Lk is the number of RAKE combining paths of user k.

(2) Output of the respreader 217 of each path is outputted from theoutput terminal 507 (507-1-507-Lk) as an interference replica ofmultipath wave of the present stage. These interference replicas are fedto the next (i+1)'th stage to be used for eliminating interferencereplicas of multipath waves.

In the ICU of FIG. 14, the interference replica eliminators 504 and 505are disposed outside and inside the ICU, but the present invention isnot limited to this configuration. In short, a signal subtracted byinterference replicas of other users and interference replicas ofmultipath waves of other paths of own channel may be subtracted from thereceived spread signal as an input signal to the matched filter 211 inthe ICU 510.

With the present embodiment, SIR can be improved even further ascompared with the first embodiment. As a result, receptioncharacteristics can be improved thereby increasing the subscribercapacity of the system.

Embodiment 5

FIG. 15 is a block diagram showing the construction of an interferencecanceler after the second stage of a fifth embodiment of the CDMAdemodulation apparatus according to the present invention. In thepresent embodiment, the decision data outputted from a data decisionblock 215 is matched in amplitude with that of a desired wave to producean interference replica of each multipath of each user in high accuracy.

A difference of the fifth embodiment shown in FIG. 15 from the fourthembodiment shown in FIG. 14 is that a circuit for determining anamplitude value of decision data is newly provided. This point will bedescribed below. A reception signal power detector 210 (521-1-521-Lk: Lkbeing the number of RAKE combining paths) determines a signal power ofdespread signal of each path. This can be determined as a square-law sumof amplitude of the in-phase component and quadrature component of thedespread signal. An adder 523 adds each output of the power detector 521of the RAKE combining multipaths to obtain a reception signal powerafter RAKE combining. An in-phase/quadrature component amplitudeconverter 525 determines absolute amplitude S of in-phase component andquadrature component of the reception signal from the reception signalpower. Since the amplitude values of individual symbols are varied bythe influence of noise, the values are averaged over 1 pilot block toobtain an amplitude value removed of the influence of noise. Theaveraging is achieved by an averaging unit 527. The averaged amplitudevalue is fed to a multiplier 529, to be adjusted so that the amplitudevalue of the decision data matches with the amplitude value of thereception signal.

With the present embodiment, interference replicas of each multipath ofeach user can be produced with good accuracy.

Embodiment 6

FIGS. 16A and 16B are block diagrams showing the construction of a firststage interference canceling block of a sixth embodiment of th CDMAdemodulating apparatus according to the present invention. Othercomponents are similar to the construction shown in FIG. 4. That is, thematched filter 103, the received level detector 104, the channel rankingunit 105, the interference canceling blocks 107 and 108 after the secondstage are similar to those in the first embodiment.

As described above, the matched filter 103 makes correlation detectionof the spreading code replica synchronized with the received spreadsignal of each path of each channel with the received spread signal S.The received level detector 104 calculates the sum of reception power ofeach path outputted from the matched filter 103 to detect the receptionsignal level of a desired wave. The channel ranking unit 105 outputschannel ranking information for controlling the order of demodulation ofusers of receiver input.

A difference of the interference canceling block of the presentembodiment from the interference canceling block shown in FIG. 5A isthat the interference canceling block of first-k'th users is constructedabout a decorrelator (decorrelation filter) as the center.

In FIGS. 16A and 16B, matched filters 601 (601-1-601-k) despread signalsof each path of k users from higher reception signal level according tothe channel ranking information supplied from the channel ranking unit105. A decorrelator 603 functions as a decorrelation filter, whichoutputs despread spectrum interference eliminated from each other usingsignals from each matched filter of each path of k users from higherreception signal level as an input spectrum according to the informationfrom the matched filter 601 and the channel ranking unit 105.

Coherent detector/interference production units 610 (610-1-610-k) hasthe same construction as the ICU 210 of FIG. 5A with the matched filter211 removed, which calculates interference replicas of the first-k'thchannels from the output signal of the decorrelator 603.

For (k+1)'th-M'th users, the procedure is similar to the correspondingportion of the first embodiment. That is, the delay unit 203, theinterference subtractor 204, and the ICU 210 are similar to those in thefirst embodiment. Thus, for k users of high reception signal level,interference replicas are estimated according to the output of thedecorrelator 603, and using the estimated interference replicas,demodulation is performed on remaining (M-k) users. Further, in theinterference canceling block after the second stage, estimatedinterference replicas of each user are calculated as in the firstembodiment. The interference canceling block 108 of the last (H'th)stage outputs the reproduction data of each user.

The decorrelator 603 makes quadrature processing on ΣLk users of highreception signal level to improve the SIR of the received spread signal.Quadrature processing by the decorrelator 603 is performed as follows.Specifically, the decorrelator 603 produces the received spreading codereplicas of each path from the spreading code of k users and thereception timing. Then, cross-correlation between ΣLk spreading codes iscalculated to produce a correlation matrix using the cross-correlationvalues. Further, an inverse matrix of this correlation matrix iscalculated and applied to reception signal vectors to make quadratureprocessing between reception signal vectors of all paths of k users.

As a result, for example, signals of each path of the first userquadrate with signals of each path of 2nd-k'th users. Therefore,interference signals to each path of the first user are only residualinterference signals from each path of (k+1) to M'th users, thus the SIRis improved. On each path of k users which is quadrature processed bythe decorrelator 603 is subjected to channel variation estimation,channel variation compensation, RAKE combining, and interference replicaproduction by the coherent detector/interference production unit 610.These interference replicas of k users are inputs to the ICUs 210-(k+1)of (k+1)'th user, which are processed as in the first embodiment.

With the present embodiment, defect of the first embodiment iseliminated. That is, the first embodiment, the user of high receptionsignal level which is subjected to interference replica estimation inthe first step has been disadvantageous. However, in the presentembodiment, since, for the first k users, interference canceling isperformed by the decorrelator 603, such a defect of the first embodimentcan be eliminated. The value of k is typically 2 or more, and less thanthe spreading factor PG, but cannot be an excessively high value. Thisis because the dimension of the matrix treated by the decorrelatorrapidly increases as the number of channels increases.

Embodiment 7

FIGS. 17A and 17B are block diagrams showing a seventh embodiment of aninterference canceling block of the CDMA demodulating apparatusaccording to the present invention. A difference of the presentembodiment from the sixth embodiment is that processing of all stages toM users is carried out by a single ICU. That is, the hardware issimplified by repeatedly using a single ICU in time division.

Since the construction and functions of the present embodiment can beeasily understood from the second and sixth embodiments, detaileddescription thereof is omitted.

Embodiment 8

FIGS. 18A and 18B are block diagrams showing an eighth embodiment of theCDMA demodulating apparatus according to the present invention.

The present embodiment is a simplification of the first embodiment shownin FIG. 4 and differs from the first embodiment in the following points.

(1) Construction of interference canceling blocks 700, 720 and 740 issimplified over the construction of the interference canceling blocks106, 107 and 108 shown in FIG. 4.

FIGS. 19A and 19B are block diagrams showing the construction of firstand second stage interference canceling blocks. However, the portionsurrounded by the broken line in FIG. 19B relates to a modification ofthe present embodiment and will be described later.

The interference canceling blocks shown in FIGS. 19A and 19B differ fromthe interference canceling blocks shown in FIG. 5A in the constructionof the ICU 710 (710-1-710-M). The ICU 710 does not performestimation/compensation and data decision of the despread signal.Specifically, the components 212-216 are omitted from the ICU 210 ofFIG. 5A. That is, the matched filter 211 of the ICU 710 despreads thereceived spread signal in each path and outputs the despread signal. Thedespread signal is fed directly to the respreader 217. The respreader217 respreads the despread signal of each path using the spreading codereplica synchronized with the received spreading code of each path toobtain the interference signal replica of each path. The adder 218determines the sum of interference signal replicas of each path. This isthe estimated interference replica S₁.sup.(1) of user 1. Thus, thesignal despread by the matched filter 211 is immediately respread by therespreader 217 to simplify the circuitry compared with the firstembodiment.

(2) The pilot interpolation/RAKE combining coherent detectors 750, 760and 770 are connected to the output side of the interference cancelingblock 740 of the last stage.

Interference-reduced signals D₁.sup.(H), D₂.sup.(H), D_(M).sup.(H) areoutputted from ICU of each channel of the interference canceling block740 of the last stage, that is, H'th stage. These signals are inputtedindividually to the pilot interpolation/RAKE combining coherentdetectors 750, 760 and 770 provided in each channel. Construction andoperation of the detector 750 is the same as the construction andoperation from the matched filter 211 to the data decision block 215 inICU 210 of the first embodiment, which will be briefly described below.

The matched filter 751 receiving the signal D₁.sup.(H) from theinterference canceling block 740 despreads the signal in each path. ThePCHE (pilot symbol channel variation estimator) 752 estimates variationof each pilot symbol, which is averaged in the pilot section to bedetermined as a phase variation estimation value. The channel variationcompensator 753 interpolates the phase variation estimation value intoeach position of information symbol sandwiched between pilot symbols toestimate the channel phase variation of each information symbol, andcompensates for channel variation of information symbol section usingthe estimation channel phase variation to the output of the matchedfilter 751. The RAKE combiner 754 makes RAKE combination of thephase-compensated signal of each path using the reception power of eachpath as weighting. The data decision block 755 decides the RAKEsynthesized signal to output reproduction data. Thus, absolutesynchronization detection is achieved.

The present embodiment, unlike the above-described other embodiments,does not perform phase estimation of each path for each user of eachstage. This considerably simplifies the construction of the interferencecanceling block of each stage. Since the interference signal replica inthe present embodiment is not subjected to data decision, it is subjectdirectly to the influence of thermal noise, however, this is nearlyequivalent to the influence of decision error when the producing thereproduction data replica in the above-described other embodiments.Further, since the reproduction data replica is not produced, it isconsidered that in the resulting interference signal replica, influenceof cross-correlation of each spreading code is transmitted to theinterference canceling block of each stage, but the influence can bereduced by suppressing the number of stages of the interferencecanceling blocks to a few stages.

In the present embodiment, the matched filter is used as despreadingmeans, however, alternatively, a serial canceler of the samecharacteristics can be constructed using a sliding correlator.

The portion surrounded by the broken line in FIG. 19B indicates amodification of the eighth embodiment. In this modification example,input signal to each ICU 730 of the interference canceling block 720 ofthe second stage is inputted to the pilot interpolation/RAKE combiningcoherent detector 750.

Embodiment 9

FIG. 20 is a block diagram showing a ninth embodiment of the CDMAdemodulating apparatus according to the present invention. The presentembodiment is a simplified example of the second embodiment shown inFIG. 10, and since construction and functions thereof are understoodfrom the second and eighth embodiments, detailed description thereof isomitted.

Embodiment 10

As described above, in DS-CDMA, each communicator is subject toinstantaneous variation due to fading, short period variation, anddistance variation. Therefore, to satisfy the desired reception qualityin a mobile station, it is necessary to make a transmission powercontrol to control the SIR in the receiver input of the base station.

Transmission power control is divided into an open loop type and aclosed loop type. In the former, SIR is measured at the receiving side,and the transmission power is controlled according to the measuredresult. In the latter, SIR is measured at the receiving side, andaccording to a difference between the measured result and a target SIRvalue, a transmission power control signal is transmitted to thetransmission counterpart to control the transmission power of thecounterpart. When there is no correlation between transmission andreception carrier levels, the closed loop type transmission powercontrol is effective.

Characteristics when the closed loop type transmission power control isapplied in CDMA mobile communications are determined mainly by controldelay.

FIG. 21 is a graph showing an example of error characteristics oftransmission power control when transmission power control delay is usedas a parameter. As the fading rate fdT (abscissas) normalized by thecontrol period of transmission power control increases, control error(ordinates) of transmission power increases. When fading exceeds acertain rate, transmission power control does not follow the fading, andthe characteristic becomes flat. Further, as the control delayincreases, the flat portion of control error increases. If transmissionpower control error increases, communication quality degrades in thesection where SIR is lower than the target value, which leads to areduction in the subscriber capacity. Therefore, it is desirable thatdelay of transmission power control be as small as possible.

On the other hand, even if transmission power control is perfect and SIRin the receiver input is guaranteed to be constant, spreading codes willnever completely quadrate with each other under multipath environment ofmobile communications. Therefore, communication is affected byinterference from other communicators, the magnitude of which is areciprocal of the spreading factor at an average per one of othercommunicators. Therefore, when the number of communicators in the samefrequency band increases, the interference signal power level increases,and the communicator capacity per cell is limited. To further increasethe communicator capacity per cell, the above-described interferencecanceling technique is used.

Since, when an interference canceler is used at the receiving side, theinterference power is reduced and the reception SIR is improved,transmission power can be reduced compared with the case where nointerference canceler is used. Therefore, interference amount to othercommunication channel is reduced, and reception SIR of eachcommunication channel is improved even further.

To efficiently utilize the SIR improvement effect by the interferencecanceler, it is necessary to measure SIR of the signal afterinterference reduction. However, the multiuser interference canceler hasprocessing delay. For example, in the multi-stage type, processing delayis increased with increases in the number of stages and the number ofusers. Further, in the decorrelator type, as the numbers of users andpaths increase, processing amount required for inverse matrixcalculation increases, further, to perform quadrature processing to aplurality of past and future symbols, a processing delay of severalsymbols is unavoidable.

As described above, characteristics of transmission power control aredetermined mainly by control delay. When SIR of the signal afterinterference reduction is measured, the control delay is considerablylarge. As a result, transmission power control error becomes large,leading to a reduction in subscriber capacity.

For the above reasons, a method in which the reception SIR improvingeffect when the multiuser interference canceler is used is applied toclosed loop transmission power control has not been disclosed. Thepresent embodiment, when the interference canceler is applied in thereceiving side, causes closed loop transmission control to efficientlyfunction, thereby achieving transmission power reduction and subscribercapacity increasing effects.

FIG. 22 is a block diagram showing an embodiment of applying thetransmission power control to the CDMA demodulating apparatus accordingto the present invention.

In FIG. 22, a matched filter 801 performs correlation detection usingthe spreading code synchronized with the reception timing of each pathof each communication channel to N (N being an integer of 2 or more)communicators communicating in the same frequency band. An SIR measuringunit 802 measures SIR of the output signal of the matched filter 801. Amultiuser interference canceler 803 outputs an interference-eliminatedsignal on each communication channel. A reception quality measuring unit814 measures the reception quality of the interference-eliminated signalof each channel outputted from the multiuser interference canceler 803.A target SIR setting unit 805 compares the reception quality outputtedfrom the reception quality measuring unit 804 with a predeterminedreception quality to set a target SIR value. A TPC (transmission powercontrol) bit production unit 806 compares the reception SIR obtainedfrom the SIR measuring unit 802 with the target SIR obtained from thetarget SIR setting unit 805 to produce a transmission power controlsignal.

FIGS. 23A and 23B are block diagrams showing details of the receptionquality measuring unit 804, FIG. 23A shows the reception qualitymeasuring unit 804 for measuring the frame error ratio to monitor thereception quality, and FIG. 23B shows the reception quality measuringunit 804 for measuring the error ratio of pilot symbol to monitor thereception quality. While transmission power control is directed tofollow momentary variation to achieve the target SIR, the receptionquality measuring unit 804 performs averaging over a relatively longtime and monitors communication quality in the output of theinterference canceler 803 to correct the target SIR value oftransmission power control. Therefore, processing delay of theinterference canceler 803 has no problem.

In FIG. 23A, a CRC check unit 811 performs CRC test (Cyclic RedundancyCheck) of reception data outputted from the multiuser interferencecanceler 803. That is, reception data is inputted to the divider circuitby the produced polynomial to decide whether the remainder is zero ornot. If the remainder is zero, it is decided that there was no frameerror in the communication path, and if the remainder is not zero, it isdecided frame error to have occurred.

A frame error calculation unit 812 calculates the number of frame errorsand outputs a frame error ratio. A frame error ratio threshold valuegenerator 813 outputs a frame error ratio threshold value. A receptionquality decision block 814 compares the frame error ratio with thethreshold value to output a signal indicating the reception quality. Atarget SIR setting unit 805 corrects a reference SIR by this signal andoutputs a corrected reference SIR.

The reception quality measuring unit 804 by the error ratio of pilotsymbol, shown in FIG. 23B, comprising the following. A pilot symbolproduction unit 821 produces a pilot symbol of a known pattern. A pilotsymbol error ratio calculation unit 822 extracts the pilot symbol fromreception data outputted from the multiuser interference canceler 803,and compares it with the pilot symbol supplied from the pilot symbolproduction unit 822 to calculate the pilot symbol error ratio.

The pilot symbol error ratio threshold value generator 823 outputs athreshold value of pilot symbol. The reception quality decision block824 compares the pilot symbol error ratio with its threshold value andoutputs a signal indicating the reception quality. The target SIRsetting unit 805 corrects the reference SIR by the signal and outputs acorrected reference SIR.

Operation of the present embodiment will be described. The matchedfilter 801 detects correlation of the received spreading code with thespreading code replica for each path of each communication channel andoutputs the despread signal of each user. The SIR measuring unit 802measures SIR of each user using the despread signal. On the other hand,the multiuser interference canceler 803 outputs theinterference-eliminated despread signal using the received spreadsignal. However, the despread signal accompanies processing delay.

The reception quality measuring unit 804 measures communication qualityof the despread signal outputted from the interference canceler 803. Themeasured communication quality is fed to the target SIR setting 805 tobe compared with a predetermined reception quality.

FIG. 24 is a schematic view comparing the output of the matched filter801 with the output of the interference canceler 803. The target SIR isset by the target SIR setting unit 805 as follows.

(1) The target SIR is set to a slightly lower value than a required SIRin the output of the interference canceler 803 in view of aninterference reduction effect by the interference canceler 803.

(2) Since the interference eliminating capability of the interferencecanceler 803 can be estimated to some extent from the number ofsimultaneous communicators, the target SIR is also set according to thenumber of simultaneous communicators.

(3) When communication quality measured by the reception qualitymeasuring unit 804 is better than the desired quality, the target SIR islowered. This prevents excessive quality of communication and allows thetransmission power to be reduced even further.

(4) On the contrary, when the communication quality measured by thereception quality measuring unit 804 is worse than the desired quality,the target SIR is increased.

(5) By repeating the correction of (3) and (4), the target SIR isconverged to a value at which the desired quality is satisfied in theoutput of the interference canceler 803.

The TPC bit production unit 806 compares the measured SIR outputted fromthe SIR measuring unit 802 with the target SIR, and when the formerexceeds the latter, sends a control signal (TPC bit) to the othercommunicator to cause the counterpart to decrease the transmissionpower. On the contrary, when the latter exceeds the former, a controlsignal is sent to the other communicator to cause it to increase thetransmission power. This can achieve closed loop transmission powercontrol which follows instantaneous variation of the transmission path.

Further, the required reception quality is set for each communicationchannel. This is because the required communication quality differsaccording to the provided service (voice transmission, imagetransmission, data transmission, and the like).

Embodiment 11

FIG. 25 is a block diagram showing another embodiment in whichtransmission power control is applied to the CDMA demodulating apparatusaccording to the present invention.

The present embodiments has the following features.

(1) The replica reproduction multistage interference canceler of thefirst embodiment is used as the multiuser interference canceler 803.

(2) A pilot symbol average error ratio measuring unit 804 for measuringthe communication quality by the pilot symbol error ratio shown in FIG.23B is used as the reception quality measuring unit 804.

Since operation of the present embodiment is understood from thedescription of embodiments 1 and 10 and FIG. 23B, it will be describedbriefly.

In each stage of the interference canceler 803, interference signalsfrom other communicators are demodulated and decided to reproducetransmission information data replicas. Interference signal replicas ofeach channel are calculated from the reproduced data replicas, andsubtracted from the reception signals to enhance SIR to the desired wavesignal to be demodulated.

On the other hand, the channel ranking unit 807 performs channel rankingto rearrange the communicators in the order of stronger reception power.According to the result, the interference canceler 803 demodulates thedesired wave signal in the order of stronger reception power. Byperforming this operation over individual stages, the later the stage,the more the SIR is improved. Further, as the accuracy of interferencesignal replica is improved in each stage of the interference canceler803, variation estimation accuracy of each channel is improved.Therefore, the interference canceling effect is improved when there area large number of communicators.

Embodiment 12

FIG. 26 is a block diagram showing a yet further embodiment in whichtransmission power control is applied to the CDMA demodulating apparatusaccording to the present invention. A difference of the presentembodiment from the embodiment 11 shown in FIG. 25 is that a receptionquality measuring unit comprising a deinterleaver 808, a Viterbi decoder809, and a frame error ratio measuring unit 810 is provided in place ofthe pilot symbol average error ratio measuring unit 804.

The same functions and effect as of embodiment 11 can also be obtainedusing this construction.

What is claimed is:
 1. A CDMA (Code Division Multiple Access)demodulating apparatus for use in a CDMA communication system thatperforms spreading information data by a spreading code faster than aninformation rate to a wideband signal and the wideband signal istransmitted to achieve multiple access transmission, wherein a pilotsymbol of know pattern is received to estimate channel variation,individual reception signals received through a plurality of channelsare compensated by the estimated channel variation, and the compensatedreception signal is demodulated to reproduce the information data,comprising:a correlation detector using a spreading code as a spreadingcode replica synchronized with a reception timing of each path of eachof the channel for correlation detection of the spreading code replicawith the reception signal of each path; a received level detector fordetermining a sum of a reception power of a corresponding path of saidcorrelation detector and detecting a desired wave reception signallevel; a channel ranking unit for controlling order of demodulation ofthe user according to the reception signal level of each user detectedby said received level detector; and an interference canceler of aplurality of stages for making interference canceling according to acontrol signal outputted from said channel ranking unit, in each of theplurality of stages, making estimation of channel variation using thepilot symbol on each channel, compensating the reception signal of thechannel by the estimated channel variation, and respreading thecompensated reception signal to produce an interference signal replica.2. The CDMA demodulating apparatus as claimed in claim 1, wherein saidinterference canceler of an i'th (i being an integer of 2 or more) stageof the plurality of stages uses the interference signal replica of eachuser estimated by the interference canceler of the (i-1)th stage as aninput to supply the interference signal replica of each user estimatedby the interference canceler of the i'th stage to said interferencecanceler of a (i+1)'th stage.
 3. The CDMA demodulating apparatus asclaimed in claim 2, wherein each of said interference canceler of eachstage comprises a sub-interference canceler for each user for producingthe interference signal replica, said sub-interference canceler of ak'th (k=any of 1, 2, . . . , M) user of said interference canceler ofthe i'th stage comprising:an interference subtractor for subtractinginterference signal replicas in said interference canceler of the i'thstage as interference signal replicas of first, second . . . and (k-1)thusers from the reception signal, subtracting interference signalreplicas in said interference canceler of an (i-1)'th stage asinterference replicas of (k+1)'th, . . . (M-1)'th and M'th users fromthe reception signal; a channel variation estimator for estimating achannel variation of the pilot symbol in the output signal of saidinterference subtractor for each path, and estimating the channelvariation by interpolating the channel variation of the estimated pilotsymbol into a position of each symbol of the information data in theoutput signal of said interference subtractor; a channel variationcompensator for compensating the reception signal for the channelvariation estimated for each path by said channel variation estimator; aRAKE combiner for synthesizing the reception signal of each pathoutputted from said channel variation compensator; a data decision blockfor deciding the output signal of said RAKE combiner; a channelvariation adder for adding a channel variation obtained as an output ofsaid channel variation estimator to the decision data outputted fromsaid data decision block; a respreader for spreading a signal of eachpath outputted from said channel variation adder by a spreading codesynchronized with reception timing of each path; and an adder for addingthe output of said respreader to produce an interference signal replicaof the k'th user.
 4. The CDMA demodulating apparatus as claimed in claim1, wherein said correlation detector comprises a plurality of matchedfilters.
 5. The CDMA demodulating apparatus as claimed in claim 1,wherein said correlation detector comprises a plurality of slidingcorrelators.
 6. The CDMA demodulating apparatus as claimed in claim 3,wherein the pilot symbol is inserted periodically between theinformation data.
 7. The CDMA demodulating apparatus as claimed in claim3, wherein said interference canceler of each stage comprises one unitof said sub-interference canceler, and memories for storing interferencereplicas of individual users of individual stages, using saidsub-interference canceler in the mode of time division.
 8. The CDMAdemodulating apparatus as claimed in claim 6, wherein said interferencecanceler uses a block as a processing unit of a block of constant timeincluding at least two adjacent pilot signal sections, and saidsub-interference canceler further comprises an extrapolating unit for aninformation symbol outside the pilot signal section for extrapolatingthe pilot symbol closest to the information symbol to determine channelvariation of the information symbol.
 9. The CDMA demodulating apparatusas claimed in claim 3, wherein a subtractor for subtracting aninterference signal replica other than of a j'th path of the k'thcommunicator in an (i-1)'th stage from the output signal of saidinterference subtractor is provided at the input side of saidcorrelation detector of the j'th (j being 1 to a path number Lk of RAKEcombining) of the k'th user of the i'th (i being an integer of 2 ormore) stage interference canceler.
 10. The CDMA demodulating apparatusas claimed in claim 3, wherein said sub-interference canceler furthercomprising:a reception signal power detector for detecting a power ofthe reception signal of each path after despreading outputted from saidcorrelation detector; an adder for adding the reception signal powers ofthe individual paths; an amplitude converter for detecting amplitudes ofin-phase component and quadrature component from the output of saidadder; an averaging unit for averaging the output signal of saidamplitude converter; and a multiplier for multiplying the decision databy an output of said averaging unit.
 11. The CDMA demodulating apparatusas claimed in claim 1, wherein said interference canceler of the firststage comprises a decorrelation filter for using a signal of each pathof K'th (K being an integer of 2 to spreading factor PG) user from thehigher reception signal level to obtain a despread output vector whichis interference removed from each other;and a coherentdetector/interference generator for estimating transmission data of Kusers outputted from said decorrelation filter and generating anestimated interference amount of each user, wherein said interferencecanceler uses the interference signal replica outputted from saidcoherent detector/interference generator as interference signal replicasof the K users to produce individual interference signals replicas ofthe remaining (M-K) users.
 12. The CDMA demodulating apparatus asclaimed in claim 11, wherein said interference canceler of i'th (i beingan integer of 2 or more) stage of the plurality of stages uses theinterference signal replica of each user estimated by said interferencecanceler of the (i-1)'th stage as an input and supplies saidinterference canceler of (i+1)'th stage with an estimated interferenceamount of each user estimated by said interference canceler of the i'thstage.
 13. The CDMA demodulating apparatus as claimed in claim 12,wherein said first stage interference canceler comprises asub-interference canceler for producing the estimated interferenceamount for each user after (K+1)'th user, and said sub-interferencecanceler of k'th (k=(K+1), (K+2), . . . , or M) user comprises:aninterference subtractor for subtracting interference signal replicas insaid interference canceler of the i'th stage as interference signalreplicas as estimated interference amounts of first, second . . . andK'th users from the reception signal, and subtracting interferencesignal replicas in said interference canceler of the first stage asinterference replicas of (K+1), . . . (k-1)'th users from the receptionsignal; a channel variation estimator for estimating a channel variationof the pilot symbol in the output signal of said interference subtractorfor each path, and estimating the channel variation of each informationsymbol by interpolating the channel variation of the estimated pilotsymbol into a position of each symbol of the information data in theoutput signal of said interference subtractor; a channel variationcompensator for compensating the reception signal for the channelvariation estimated for each path by said channel variation estimator; aRAKE combiner for synthesizing the reception signal of each pathoutputted from said channel variation compensator; a data decision blockfor deciding the output signal of said RAKE combiner; a channelvariation adder for adding a channel variation obtained as an output ofthe channel variation estimator to the decision data outputted from saiddata decision block; a respreader for spreading a signal of each pathoutputted from said channel variation adder by a spreading codesynchronized with reception timing of each path; and an adder for addingthe output of the respreader to produce an interference signal replicaof the k'th user, wherein each of said interference canceler of andafter the second stage comprises a sub-interference canceler for eachuser for producing the interference signal replica, saidsub-interference canceler of a k'th (k=any of 1, 2, . . . , M) user ofsaid interference canceler of the i'th stage comprising: an interferencesubtractor for subtracting interference signal replicas in saidinterference canceler of the i'th stage as interference signal replicasof first, second . . . and (k-1)th users from the reception signal, andsubtracting interference signal replicas in said interference cancelerof an (i-1)'th stage as interference replicas of (k+1)'th, . . .(M-1)'th and M'th users from the reception signal; a channel variationestimator for estimating a channel variation of the pilot symbol in theoutput signal of said interference subtractor for each path, andestimating the channel variation of the information symbol byinterpolating the channel variation of the estimated pilot symbol into aposition of each symbol of the information data in the output signal ofsaid interference subtractor; a channel variation compensator forcompensating the reception signal for the channel variation estimatedfor each path by said channel variation estimator; a RAKE combiner forsynthesizing the reception signal of each path outputted from saidchannel variation compensator; a data decision block for deciding theoutput signal of said RAKE combiner; a channel variation adder foradding a channel variation obtained as an output of said channelvariation estimator to the decision data outputted from said datadecision block; a respreader for spreading a signal of each pathoutputted from said channel variation adder by a spreading codesynchronized with reception timing of each path; and an adder for addingthe output of said respreader to produce an interference signal replicaof the k'th user.
 14. The CDMA demodulating apparatus as claimed inclaim 11, wherein said correlation detector comprises a plurality ofmatched filters.
 15. The CDMA demodulating apparatus as claimed in claim11, wherein said correlation detector comprises a plurality of slidingcorrelators.
 16. The CDMA demodulating apparatus as claimed in claim 13,wherein the pilot symbol is inserted periodically between theinformation data.
 17. The CDMA demodulating apparatus as claimed inclaim 13, wherein said interference canceler of each stage comprises oneunit of said sub-interference canceler, and memories for storinginterference replicas of individual users of individual stages, usingsaid sub-interference canceler in the mode of time division.
 18. TheCDMA demodulating apparatus as claimed in claim 11, wherein saidcoherent detector/interference generator comprises:a channel variationestimator for estimating a channel variation of the pilot symbol in theoutput signal of said interference subtractor for each path, andestimating the channel variation of each information symbol byinterpolating the channel variation of the estimated pilot symbol into aposition of each symbol of the information data in the output signal ofsaid interference subtractor; a channel variation compensator forcompensating the reception signal for the channel variation estimatedfor each path by said channel variation estimator; a RAKE combiner forsynthesizing the reception signal of each path outputted from saidchannel variation compensator; a data decision block for deciding theoutput signal of said RAKE combiner; a channel variation adder foradding a channel variation obtained as an output of said channelvariation estimator to the decision data outputted from said datadecision block; a respreader for spreading a signal of each pathoutputted from said channel variation adder by a spreading codesynchronized with reception timing of each path; and an adder for addingthe output of the respreader to produce an interference signal replicaof the k'th user.
 19. The CDMA demodulating apparatus as claimed inclaim 1 further comprising:an SIR measuring unit for measuring an SIR ofthe output of said correlation detector; a reception quality measuringunit for measuring a reception quality of the output signal of saidinterference canceler; a target SIR setting unit for setting a targetSIR according to the measured reception quality and a required receptionquality; and a transmission power control signal generator for comparingSIR outputted from said SIR measuring unit with the target SIR.
 20. TheCDMA demodulating apparatus as claimed in claim 19, wherein said SIRsetting unit sets an initial value of the target SIR according to thenumber of simultaneous communicators.
 21. The CDMA demodulatingapparatus as claimed in claim 19, wherein said reception qualitymeasuring unit comprises an error ratio measuring unit for measuring aframe error ratio, and means for comparing the frame error ratio with apredetermined threshold value of frame error ratio to decide thereception quality.
 22. The CDMA demodulating apparatus as claimed inclaim 19, wherein said reception quality measuring unit comprises anerror ratio measuring unit for measuring a bit error ratio of the pilotsymbol, and means for comparing the bit error ratio with a predeterminedthreshold value of bit error ratio to decide the reception quality. 23.The CDMA demodulating apparatus as claimed in claim 19, wherein saidcorrelation detector is a matched filter.
 24. The CDMA demodulatingapparatus as claimed in claim 23, wherein said interference cancelercomprises a reception vector generator for generating a reception vectorcomprising despread signal of each path for each channel from the outputsignal of said matched filter, a cross-correlation inverse matrixgenerator for calculating cross-correlation of all spreading codes otherthan the spreading code of own channel and receiver input to produce aninverse matrix of a matrix comprising cross-correlation, and a matrixvector multiplier for compensating the reception vector by the inversematrix to remove cross-correlation between individual reception vectorsthereby removing interference.
 25. A CDMA (Code Division MultipleAccess) demodulating apparatus for use in a CDMA system that performsmultiple access transmission by transmitting a spread signal, the spreadsignal being generated by spreading information data into a widebandsignal with a spreading code whose rate is higher than an informationrate, wherein a pilot symbol of a known pattern to estimate a channelvariation, each reception signal received through a plurality ofchannels is compensated by the estimated channel variation, and thecompensated reception signal is demodulated to reproduce the informationdata, the demodulating apparatus comprising:a correlation detector,using a spreading code in phase with reception timing of each path ofeach channel, for detecting correlation of the spreading code with thereception signal of each path; a received level detector for determininga sum of a reception power of a corresponding path of the correlationdetector and detecting a desired wave reception signal level; a channelranking unit for controlling order of demodulation of the user accordingto the reception signal level of each user detected by said receivedlevel detector; an interference canceler of a plurality of stages fordespreading the reception signal for individual users according to anorder determined by the control signal outputted from said channelranking unit, respreading the despread signal, and subtracting aninterference signal replica of other users obtained by respreading fromthe reception signal of the corresponding user; and a pilotinterpolation/coherent detector for estimating a channel variation usingthe pilot symbol in the signal after subtracting by an interferenceamount of other users in said interference canceler of the last stage inthe plurality of stages, compensating the information data using theestimated channel variation to perform absolute synchronizationdetection of the compensated information data.
 26. The CDMA demodulatingapparatus as claimed in claim 25, wherein an i'th (i being an integer of2 or more) stage interference canceler uses the interference signalreplica of each user estimated in the (i-1)'th stage interferencecanceler as an input to supply the interference signal replica estimatedin said i'th stage interference canceler to the (i+1)'th stageinterference canceler.
 27. The CDMA demodulating apparatus as claimed inclaim 26, wherein each interference canceler of each of the stagescomprises a sub-interference canceler for each user for producing theinterference signal replica, said sub-interference canceler of a k'th(k=1, 2, . . . , or M) user of said i'th stage interference cancelercomprising:an interference subtractor for subtracting interferencesignal replicas in said interference canceler of the i'th stage asinterference signal replicas of first, second . . . and (k-1)th usersfrom the reception signal, subtracting interference signal replicas insaid interference canceler of an (i-1)'th stage as interference replicasof (k+1)'th, . . . (M-1)'th and M'th users from the reception signal; amatched filter for making correlation detection between the outputsignal of said interference subtractor and a spreading code replica inphase with reception timing of each path to obtain a despread signal ofeach path; and a respreading/combiner unit for spreading the despreadsignal of each path with a spreading code in phase with the receptiontiming of each path, estimating an interference signal replica of thepath of each user, and adding the estimated interference signal replicato produce an interference signal replica of each user.
 28. The CDMAdemodulating apparatus as claimed in claim 25, wherein the pilot symbolis inserted periodically between the information data.
 29. The CDMAdemodulating apparatus as claimed in claim 25, wherein said interferencecanceler of each stage comprises one unit of said sub-interferencecanceler, and memories for storing interference replicas of individualusers of individual stages, using said sub-interference canceler in themode of time division.